This invention relates to a thermal transfer image-receiving sheet which, in use, is superposed onto a thermal dye donor sheet, and more particularly to a thermal transfer image-receiving sheet having texture similar to plain paper.
Various thermal transfer recording systems are known in the art. Among them, a thermal dye transfer system, wherein a sublimable dye as a colorant is transferred, using a thermal head capable of generating heat in response to a recording information, onto an image-receiving sheet to produce an image.
According to this recording system, since a sublimable dye is used as a colorant, density gradation can be controlled as desired and can reproduce a full-color image of an original image. Further, the formed dye image is very sharp and highly transparent and hence is excellent in reproduction of halftone and gradation, realizing a high-quality image comparable to a silver-salt photographic image.
A plastic sheet, a laminate sheet composed of a plastic sheet and paper or the like, or a synthetic paper or the like has been used as a thermal transfer image-receiving sheet in the thermal dye transfer system. In order to spread utilization of the thermal dye transfer system to general offices, use of plain papers, such as coated paper (art paper), cast coated paper, and paper for PPC, as a substrate sheet for the image-receiving sheet has been proposed in the art. In forming a dye-receptive layer on the surface of the plain paper as the substrate sheet, good heat insulating properties are required of the substrate sheet from the viewpoint of improving the sensitivity in printing. In order to improve the heat insulating properties, a proposal has been made on provision of a heat insulating layer between the substrate sheet and the dye-receptive layer (Japanese Patent Laid-Open Publication No. 155942/1994).
In a thermal transfer image-receiving sheet comprising the conventional paper substrate and, provided on the substrate in the following order, a heat-insulating, porous layer composed mainly of a resin and a dye-receptive layer, formation of the dye-receptive layer by coating a solution of a resin in an organic solvent poses a problem that, due to poor solvent resistance of the heat-insulating, porous layer, the porous structure of the heat-insulating, porous layer is destroyed by the organic solvent in the course of coating of the coating liquid for the dye-receptive layer, making it impossible to print an image having satisfactory quality and density.
Provision of a solvent barrier layer comprising polyvinyl alcohol between the porous layer and the dye-receptive layer is considered effective for solving the above problem (Japanese Patent Laid-Open Publication No. 144394/1986). In this case, the adhesion between polyvinyl alcohol and the resin used in the dye-receptive layer is so low that the adhesion between the barrier and the dye-receptive layer is adversely affected.
Accordingly, an object of the present invention is to solve the above problems of the prior art and to provide a thermal transfer image-receiving sheet which does not cause destruction of a heat-insulating, porous layer at the time of formation of a dye-receptive layer, has no fear of the dye-receptive layer being separated, and in addition can produce a printed image having satisfactory image quality and density.